1. Field of the Invention
The present invention relates to an optically writable record of digital information, and more particularly is directed to a writable record disk of the type in which program data together with respective address data are recorded along a spiral track in an annular recording area.
2. Description of the Prior Art
In a so-called compact disk (CD) having digitized audio signals recorded as a plurality of sectional program data on a rotatable disk-like recording medium so as to be optically readable, the recording format is standardized and the plurality of sectional program data are recorded together with address data along a spiral track in a main annular recording area, while table-of-contents data (hereinafter referred to as TOC data) identifying the sectional program data in the main recording area are recorded along a spiral track in another annular recording area, termed a lead-in area, and which is located radially inside the main recording area in surrounding relation to a central aperture. Furthermore, another annular area, termed a lead-out area, is formed around the outer periphery of the main recording area. Reproduction of the program data from such compact disk (CD) is performed by means of a CD player, which is also standardized so as to be compatible with the standardized compact disk.
After manufacture of such compact disk as a complete product, no further or other data is recordable on the disk and, therefore, it is used merely for reproduction of the data already recorded thereon. In contrast with such read-only type of compact disk, a writable-type disk has been proposed which permits new data to be additionally recorded and then reproduced by the use of a laser light beam after manufacture as a complete or already recorded optical disk.
There is also known a post-writable record disk which permits data to be recorded thereon only once after completion as a final product. In such post-writable record disk, a guide groove for defining a record track is provided in a recording area where program data together with respective address data are to be recorded, and such recording area includes a main recording area, a lead-in area radially inside the main recording area and surrounding a central aperture, and a PG,4 lead-out area formed around the outer periphery of the main recording area.
Recording of data on a post-writable record disk is effected by a light beam which is modulated in accordance with the data to be recorded and is projected to be incident upon positions which are predetermined in the recording area by a guide groove there provided. The resulting data-recorded region in the recording area has a light reflectance or reflection factor different from that of any other region of the disk. After such recording on a post-writable record disk, the light reflectance in its recording area is generally lower than that in a pre-recorded compact disk, so that the amount of read light reflected from the post-writable record disk is usually insufficient for reproduction by an ordinary CD player. For example, in the conventional optically post-writable record disk, the reflectance or reflection factor at the recorded area generally ranges from 15 to 45 per cent, whereas the prerecorded compact disk has a reflection factor exceeding 70 percent for ensuring reliable reproduction by a conventional CD player.
Although post-writable record disks of a high reflectance type have been recently proposed in which, after recording of data in the recording area, the latter has an adequately high light reflectance to ensure a sufficient amount of read light for a conventional CD player, such post-writable record disks are otherwise unsuitable for reproducing or playback in conventional CD players. More specifically, in reproducing program data from a prerecorded compact disk by a CD player, one of the important advantages has been the relatively quick access that is had to the plurality of sectional program data recorded on the compact disk. In achieving such ready access to the recorded plurality of program data, reference is made to the TOC data also recorded on the compact disk. Therefore, even if a post-writable record disk of high reflectance type retains a sufficiently high light reflectance for providing an ample amount of read light to a CD player from the region in which a plurality of sectional program data are recorded, it is still necessary, for the purpose of enabling ready access to the recorded sectional program data by the conventional CD player, that TOC data identifying such plural program data be recorded in a lead-in area, that is, similarly to the case of a prerecorded compact disk.
In an attempt to satisfy the foregoing, a technique has been proposed, for example, as disclosed in Japanese Laid Open Patent No. 61 (1986)-224186, for recording TOC data in the lead-in area of a writable record disk. However, such proposed technique for recording TOC data in the lead-in area of a writable record disk fails to maintain strict positional control with regard to the end portion of the lead-in area where the TOC data are recorded and also with regard to the data-recording start position in the main recording area extending around the lead-in area. As a result, a blank or non-recorded space is formed between the TOC-data recorded region of the lead-in area and the program-data recorded region of the main recording area, and such blank space may act as an impediment to proper reproduction of the data by a CD player.